The invention relates to a switch controller system for converting an input voltage (U.sub.E) into an output voltage (U.sub.A) including a control amplifier and a pulse width modulator in the control loop as well as a power output stage including a storage choke (L) as the control path
Switch controllers are used primarily as direct voltage converters for low to medium power applications. If the input voltage range lies above the output voltage, down converters are employed in the switch controllers. If, on the other hand, the input voltage range is lower than the output voltage, up converters are employed. Such switch controllers are disclosed, for example, by U. Tietzen, Ch. Schenk, in Halbleiterschaltungstechnik [Semiconductor Circuit Technology], Berlin, 1989, Chapter 18.6, pages 563-571. The down converter disclosed there is composed of a series connection of a series switch with a storage choke. The input of the storage choke is connected to ground potential by way of a reverse direction diode. The output voltage is obtained at the output of coil L. A smoothing capacitor determines the ripple of the output voltage. For the up converter, the storage choke receives the input voltage directly. At its output, the storage choke is connected to ground by way of a ground switch. The output voltage U.sub.A is tapped by way of a diode in forward direction. A smoothing capacitor here again takes care of reducing the output ripple. In order to prevent the output voltage from rising if the output currents are low, the ratio of turn-on time to turn-off time for the up converter and the down converter must be adapted accordingly. The generation of the pulse width modulated switching signal is effected by means of two modules: a control amplifier with voltage reference and a pulse width modulator. The pulse width modulator is generally composed of a sawtooth generator and a comparator. The comparator switches the switch on as long as the control voltage is greater than the delta voltage. The control voltage resulting therefrom is a rectangular voltage at a fixed frequency whose keying ratio is a function of the control voltage. Integrated pulse width modulators for switch controllers are known, for example, from Unitrode, Semiconductor Databook, 1987-1988, pages 12-6 to 12-11.
These known switch controllers have the drawback that, depending on whether the input voltage range lies above or below the output voltage, either a down converter or an up converter is employed in the switch controller.